This invention relates to a process for producing cement clinker wherein raw particulate matter or meal is fed to a heat exchanger, heat is supplied to the heat exchanger from a downstream furnace, the raw particulate matter is heated in the heat exchanger, and the heated raw particulate matter is conveyed to the furnace and is sintered therein by use of a fuel to form cement clinker.
It is known that cement clinker can be produced from raw particulate material in rotary cylindrical kilns and fluidized bed furnaces. After sintering or calcining, the cement clinker is cooled. The cooled cement clinker is then finely ground for use in the production of cement, setting control agents or other agents being added during the grinding process. The raw particulate matter is, for example, limestone, clay, iron oxide and sand.
To produce the high flame temperatures (above 2000.degree. C.) required for calcining or sintering the cement clinker, pulverized coal, oil or gas are used as high grade fuels. It is also known to use electrical energy for this purpose (see "Schweizerische Bauzeitung" 66, 1948, p. 465). These high grade forms of energy are expensive.
It is further known to use lower-grade fuels instead of the expensive forms of energy given above. Examples of such low-grade fuels are oil shale, wash mine waste and bituminous limestone (see German Pat. No. 1,251,688). However, the lower grade fuels can only be used to a limited extent for the calcination process, namely in the low temperature range. For an endothermic process at low temperature, a high amount of heat is needed, and the ash constituents remain in the clinker mixture.
For the high temperature range in which the sintering and formation of the clinker minerals is effected, only the aforementioned expensive high grade fuels have hitherto been used, since the flame temperatures which can be obtained depend on the calorific value of the fuel and on the excess of air.
The object of the invention is to create a process of the type specified above wherein economical fuels can be used, particularly for the high temperature range, for sintering the cement clinker.